1. Field of the Invention:
This invention relates to a hydrogenated petroleum resin and the process for preparing the same. More particularly, the invention is directed to a hydrogenated petroleum resin which is suitably used as a tackifier The resin is prepared by first cationically polymerizing a mixture of an aliphatic hydrocarbon fraction comprising piperylene, isoprene, and monoolefins, and an aromatic monoolefin using a Friedel Crafts catalyst to produce a precursor copolymer petroleum resin, and then hydrogenating this precursor copolymer petroleum resin to substantially saturate unsaturated bonds derived from the aliphatic di-and monoolefins, but leaving a certain proportion of aromatic nuclei unhydrogenated.
2. Description of the Background:
Conventionally, rosin-type or terpene-type resins which are derived from naturally occurring materials have widely been used as tackifiers in adhesion technologies such as pressure-sensitive adhesion and hot-melt adhesion. These materials, however, are not stably available nor free from price fluctuation. Because of these reasons, increased attention is being given to petroleum hydrocarbon resins. Recent developments in adhesion technology as well as diversified use of adhesives, however, is demanding more sophisticated performance of the tackifing resins. Examples of such performance include excellent heat stability and weather resistance under severer conditions, and better compatibility with polar polymers such as ethylene-vinyl acetate copolymer (EVA), SBR, styrene-type thermoplastic elastomer, and the like. Other requirements are providing an attractive color for a better appearance of the product and a more pleasant odor during handling.
In order to satisfy these diverse requirements assessed on the adhesive compounds, attempts have been undertaken to develop hydrogenated petroleum resins by hydrogenating conventional petroleum resins. Hydrogenating aliphatic hydrocarbon resins for improving their heat stability is known in the art (U.S. Pat. No. 2,824,860). Even though some degree of improvement over the precursor petroleum resins before hydrogenation has been realized in these known hydrogenated petroleum resins in terms of color, odor, or heat stability, their performance qualities such as adequate heat stability, compatibility with polar polymers, or the like, are yet to be improved to satisfy the recent demand in the adhesives industries. Specifically, there are conventionally known hydrogenated petroleum resins exhibiting either excellent heat stability or compatibility with polar polymers, but none of them possess these two required characteristics at the same time.
In view of this situation, the present inventors have conducted extensive studies to improve these defects in the conventional hydrogenated petroleum resins, and to obtain an odorless and transparent hydrogenated petroleum resin which possesses both of the two essential requirements, i.e., excellent heat stability and compatibility with polar polymers.
The problem in the conventional hydrogenated petroleum resins with respect to the poor heat stability or insufficient compatibility with polar polymers is considered to be caused by improper selection of raw material hydrocarbon fractions which ultimately constitute the hydrogenated petroleum resins. In line with this presumption, a number of combinations of a variety of petroleum hydrocarbon fractions were studied. As a result, a certain combination of a C.sub.5 fraction, containing diolefins and monoolefins in a specific proportion and an aromatic monoolefin, was found to give an optimum construction of a polymer resin. It was further found that the polymer resin thus obtained, when properly hydrogenated, produces an ideal petroleum resin which satisfies both of the requirements of heat stability and compatibility with polar polymers. Such findings have led to the completion of this invention.